It's your (shared) responsibility to determine what done is, and you should have a hand in estimating how long tasks will take. In my opinion, you as the engine

It's your (shared) responsibility to determine what done is, and you should have a hand in estimating how long tasks will take. In my opinion, you as the engineer are ultimately the one who decides what quality you will accept. Instead of saying/thinking "it's done, but I'm not happy with the code quality yet", just say "it's not done yet". I also firmly believe you should review all code before you commit it (would you skip proof-reading a paper before turning it in?), and that's an excellent time to spot easy improvements, places that need documentation, code that doesn't make sense, etc.